A unique phase behavior of random copolymer of N-isopropylacrylamide and N,N-diethylacrylamide in water

Abstract Thermosensitive phase separation of aqueous solutions of the random copolymers of N -isopropylacrylamide (iPA) and N , N -diethylacrylamide (dEA) (PiPA–dEA) and of iPA and N -isopropylmethacrylamide(iPMA) (PiPA–iPMA) with different compositions has been investigated by using calorimetry, turbidimetry and infrared spectroscopy. Though the phase transition temperature ( T p ) of PiPA–iPMA is a linear function of its composition, a deviation from additivity is observed for that of PiPA–dEA, that is, it has a minimum value at iPA/dEA = 1 (mol/mol). IR spectrum at the amide II mode of the copolymer suggests that part of N–H groups of iPA units form a hydrogen bond with C O groups of dEA units at T  >  T p as well as with those of the iPA units. Effects of methanol on T p of these copolymers have also been studied.

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